1. Field of the Invention
The present invention relates to a method of verifying resolution of a patterned figure, i.e., a photo resist pattern that is made by performing photolithography using a mask pattern in the step of photolithography, and a method of forming a semiconductor pattern. More particularly, the present invention relates to a method of verifying resolution of a patterned figure by detecting in advance a portion of the patterned figure with inadequate resolution to improve efficiency in device development, and a semiconductor pattern forming method for forming a pattern on a semiconductor substrate employing the above method of verifying resolution of the patterned figure.
2. Description of the Background Art
To accomplish still higher degree of integration in semiconductor integrated circuits, miniaturization of patterns has been proceeded. It thus is important, in a series of manufacturing steps of a semiconductor integrated circuit, to evaluate in advance a final shape of a photo resist pattern in the step of photolithography among others, to conduct such miniaturization of the pattern efficiently. An example of the evaluation method of a final shape of photo resist employing a conventional simulation technique will now be described with reference to attached drawings.
FIG. 19 is a flowchart of such simulation. Referring to FIG. 19, first in step SS1, data is set for a designed, patterned figure on a mask. Next, in step SS2, based on the data for the designed, patterned figure, optical image intensity distribution in an image plane (wafer surface) is obtained by optical image calculation. In step SS3, the obtained optical image intensity distribution is compared with the data for the designed, patterned figure to compute a contour line of light intensity having an equal intensity (hereinafter, referred to as a xe2x80x9ccontourxe2x80x9d) that best matches the designed, patterned figure. A figure according to the obtained contour has been used as an outline of a final pattern of photo resist.
In a practical wafer process, etching is conducted using as a mask a photo resist pattern formed on a substrate. When etching, however, the photo resist itself is subjected to etching, and thus, its film thickness gradually decreases, or, film thinning occurs. If the photo resist does not have a prescribed film thickness, a part of the photo resist pattern will be lost on the way of etching, and therefore, a desired pattern may not be formed on the substrate.
In addition, if there exists photo resist left between photo resist patterns, neighboring patterns that should naturally be separate may combine together, so that a prescribed photo resist pattern will not be formed on the substrate.
Therefore, in the step of photolithography, the photo resist pattern must be formed to have a prescribed film thickness in the region where the photo resist should be left, and the photo resist must be completely removed from the region in which it should not be left.
The above problems arise due to inadequate resolution of the photo resist in the step of photolithography. Accordingly, it is important to evaluate in advance a shape of photo resist pattern, so as to detect a portion with such inadequate resolution and to dispose a designed, patterned figure free from such deficiency in resolution.
The evaluation according to the conventional simulation as described above, however, only obtained a final shape (outline) of photo resist, and was unable to determine the resolution of the photo resist. It thus was necessary to evaluate the resolution of the photo resist by actually forming the photo resist pattern using, for example, an appropriate test pattern.
As a result, time-consuming pattern designing was required, and efficient semiconductor device development was hindered.
The present invention is made to solve the above-described problems.
An object of the present invention is to provide a method of verifying resolution of a patterned figure that allows a portion with inadequate resolution to be detected in a photo resist that corresponds to a designed, patterned figure. Another object of the present invention is to provide a method of forming a semiconductor pattern utilizing that method of verifying resolution of a patterned figure.
The method of verifying resolution of a patterned figure according to an aspect of the present invention includes the following steps. Data is set for a designed, patterned figure on a mask. Based on the data for the designed, patterned figure, optical image intensity distribution on a substrate is examined. The optical image intensity distribution and the data for the designed, patterned figure are compared to calculate data for a first contour figure having a first light intensity and best matching the designed, patterned figure. Data for an under-sized figure having the designed, patterned figure contracted by a prescribed amount and data for an over-sized figure having the designed, patterned figure expanded by a prescribed amount are calculated, which are to be used as indices when forming the designed, patterned figure as a photo resist pattern. Computed from the optical image intensity distribution are data for a second contour figure having a second light intensity that is equivalent to the light intensity with which substantially the entire photo resist film coated on the substrate is to be dissolved completely, and data for a third contour figure having a third light intensity that is equivalent to the light intensity with which substantially no photo resist film is to be dissolved. The data for the under-sized figure and the data for the third contour figure are compared to check whether the under-sized figure is included in the third contour figure, and the data for the over-sized figure and the data for the second contour figure are compared to check whether the second contour figure is included in the over-sized figure, thereby determining adequateness of the resolution of the designed, patterned figure. If the resolution of the designed, patterned figure is inadequate, information on a portion with such inadequate resolution is output.
According to this method, data for virtual under-sized and over-sized figures, and for the second and third contour figures are calculated, which are to be used as indices for determining whether a photo resist pattern can be obtained with adequate resolution corresponding to the designed, patterned figure. The second contour figure is a figure outside which substantially the entire photo resist is supposed to be completely dissolved. The third contour figure is a figure within which substantially no photo resist is considered to be dissolved. The under-sized figure is theoretically the smallest of the photo resist pattern that may be produced with adequate resolution corresponding to the designed, patterned figure, and the over-sized figure is the largest of the same. Therefore, if the under-sized figure is included in the third contour figure and the second contour figure is included in the over-sized figure, it can be determined that the resolution in the photo resist pattern corresponding to the designed, patterned figure is satisfactory. In contrast, if even one of those two conditions described above is not satisfied, the resolution of the photo resist pattern corresponding to the designed, patterned figure is determined as unsatisfactory, and information on a portion with such inadequate resolution is output. As explained above, the resolution of the designed, patterned figure can easily be determined, and if the resolution is inadequate, the designed, patterned figure can be modified based on the information on the portion with such inadequate resolution, and then the process for checking the resolution may be repeated again. A designed, patterned figure thus can be determined efficiently.
Preferably, the prescribed amount used in the step of calculating the data for under-sized figure is less than 50% of the minimum dimension of the designed, patterned figure.
This is because, if the prescribed amount is equal to or more than 50% of the minimum dimension, an under-sized figure corresponding to the designed, patterned figure cannot be acquired in a portion having that minimum dimension.
Preferably, the prescribed amount used in the step of calculating the data for over-sized figure is less than 50% of the minimum distance between neighboring patterns in the designed, patterned figure.
This is because, if the prescribed amount is equal to or more than 50% of the minimum distance, an over-sized figure corresponding to the designed, patterned figure cannot be obtained in a portion having that minimum distance.
When a positive photo resist is used, the light intensity of the first contour figure best matching the designed, patterned figure is set, in a relation between light intensity of exposed light and a dissolution rate of photo resist, equal to the light intensity at which the dissolution rate of the positive photo resist starts to increase as the light intensity increases. When a negative photo resist is used, the light intensity of the first contour figure is set equal to the light intensity with which the dissolution rate of the negative photo resist no longer decreases as the increase in light intensity.
Preferably, the second light intensity is set, in the relation between the light intensity of the exposed light and the dissolution rate of the photo resist, equal to the light intensity with which the dissolution rate of the photo resist is sufficiently high, and the dissolved amount that is a product of developing time and the dissolution rate is sufficiently large compared to the film thickness of the photo resist coated and formed on the substrate.
In this case, substantially the entire photo resist outside the second contour figure is supposed to be dissolved completely.
More preferably, the dissolved amount of photo resist is to be more than five times the film thickness of the photo resist coated and formed on the substrate.
In this case, the photo resist between neighboring patterns can be removed reliably.
Preferably, the third light intensity is set, in the relation between the light intensity of the exposed light and the dissolution rate of the photo resist, equal to the light intensity with which the dissolution rate of photo resist is sufficiently low and the dissolved amount that is a product of the developing time and the dissolution rate is sufficiently small with respect to the film thickness of the photo resist coated and formed on the substrate.
In this case, substantially no photo resist within the third contour figure is supposed to be dissolved.
More preferably, the dissolved amount of the photo resist is equal to or less than 20% of the film thickness of the photo resist coated and formed on the substrate.
In this case, when etching using the photo resist pattern as a mask, a sufficient amount of photo resist can be left even there occurs the film thinning of the photo resist.
The method of verifying resolution of a patterned figure according to another aspect of the present invention includes the following steps.
Data is set for a designed, patterned figure on a mask. Based on the data for the designed, patterned figure, optical image intensity distribution on a substrate is examined. The optical image intensity distribution and the data for the designed, patterned figure are compared to calculate data for the first contour figure having the first light intensity and best matching the designed, patterned figure. Further calculated are data for the second contour figure having the second light intensity that is equal to the light intensity with which substantially the entire photo resist coated on the substrate is to be dissolved completely, and data for the third contour figure having the third light intensity that is equal to the light intensity with which substantially no photo resist coated on the substrate is to be dissolved. The total number of component figures in the first contour figure, the total number of component figures in the second contour figure, and the total number of component figures in the third contour figure are respectively compared with the total number of component figures in the designed, patterned figure to check whether they match or not, to determine adequateness of the resolution of the designed, patterned figure. If the resolution of the designed, patterned figure is determined as inadequate, information on that is output.
According to this method, data for the first, second, and third contour figures are calculated. The first contour figure is a figure that has the first light intensity and best matches the designed, patterned figure. The second contour figure is a figure outside which substantially the entire photo resist is supposed to be dissolved completely. The third contour figure is a figure within which substantially no photo resist is considered to be dissolved. Therefore, if a portion in which photo resist should be left and a portion from which photo resist should be removed correspond to the designed, patterned figure, each of the total number of component figures within the first, second, and third contour figures must be consistent with the total number of component figures in the designed, patterned figure. If the total numbers of component figures within the first, second and third contour figures do not match the total number of component figures in the designed, patterned figure, respectively, it is considered that two component figures that are originally separate are counted as one component figure because, for example, neighboring patterns are combined together. The photo resist is thus determined as having deficiency in resolution. As a result, though information on a portion where the resolution is inadequate cannot be obtained, adequateness of the photo resist resolution can easily be determined, thereby allowing efficient device development.
The method of forming a semiconductor pattern according to yet another aspect of the present invention includes the following steps. Data is set for a designed, patterned figure on a mask. Based on the data for the designed, patterned figure, optical image intensity distribution on a substrate is examined. The optical image intensity distribution and the data for the designed, patterned figure are compared to calculate data for the first contour figure having the first light intensity and best matching the designed, patterned figure. Further calculated are data for the second contour figure having the second light intensity that is equivalent to the light intensity with which substantially the entire photo resist film coated on the substrate is dissolved completely, and data for the third contour figure having the third light intensity that is equivalent to the light intensity with which substantially no photo resist film is dissolved. Data for an under-sized figure having the designed, patterned figure contracted by a prescribed amount and data for an over-sized figure having the designed, patterned figure expanded by a prescribed amount are also calculated. The data for the under-sized figure and the data for the third contour figure are compared to check whether the under-sized figure is included within the third contour figure, and the data for the over-sized figure and the data for the second contour figure are compared to check whether the second contour figure is included within the over-sized figure, thereby determining adequateness of the resolution of the designed, patterned figure. A designed, patterned figure on a mask is determined based on the data on the adequateness of the resolution of the designed, patterned figure. A mask having the designed, patterned figure thus determined is then produced. Using this mask, photolithography and processing are conducted for patterning a film formed on a semiconductor substrate.
According to this method, the method of verifying the resolution of a patterned figure in one aspect of the present invention can be utilized when forming a semiconductor pattern. This results in efficient device development, and leads to reduction in development time and cost.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.